What the Obama administration is doing is allowing certain unauthorized immigrants to apply for something called “deferred action.” Deferred action offers protection from deportation for a certain amount of time — in this case, three years. The administration is also issuing work permits, which allow people to work in the US legally, to immigrants who receive deferred action.
But deferred action, even with a work permit, isn’t the same as legal status. Immigrants who get deferred action are still unauthorized. They’re not legal, and they’re not getting a path to citizenship.
Legal status is a term that means specific things in immigration law. The executive branch is allowed to decide who should and shouldn’t be deported, and even decide to protect immigrants in the second category from deportation temporarily, but only Congress can decide who should qualify for legal status.
Why does this matter? For one thing, legal status is much harder to take away, but deferred action can be taken away very easily. A future president could easily strip protection from deportation to all the immigrants covered by the Obama administration, which would allow them to be deported again. That wouldn’t be the case if immigrants were getting legalized through the new program.